In situ study of phase transformations in electron beam additive manufactured Ti-6Al-4 V titanium alloy by high temperature synchrotron X-ray diffraction and TEM

Abstract

The microstructure and phase composition of the EBAM Ti-6Al-4 V alloy samples were studied by the methods of in situ high temperature synchrotron X-ray diffraction and transmission electron microscopy (TEM) during heating from room temperature to a temperature of 1373 K. In the initial state, the main phase of the EBAM Ti-6Al-4 V alloy the samples was the α phase, the second phases were β + α″. The volume fraction of the β phase does not exceed 5%, α″ - 3%. It was found that the new α″ phase was formed at the temperature of 1073 K due to the phase transition α→α″. The α″ phase volume fraction increased as the heating temperature increased to the temperature of 1223 K and then decreased with a further increase of the temperature due to the α″→β phase transition. The dependences of the lattice parameters of the α, β and α″ phases on the heating temperature were revealed. It was established that the crystal lattice of the α phase was distorted during heating. The α phase passed into the unstable state. An increase of the c/a parameters ratio was accompanied by the formation of the α″ and β phases.